Electron tunneling through atomically flat and ultrathin hexagonal boron nitride

Lee, Gwan Hyoung; Yu, Yeonsil; Lee, Changgu; Dean, Cory; Shepard, Kenneth L.; Kim, Philip; Hone, James

doi:10.1063/1.3662043

Cited by 446 publications

(496 citation statements)

References 28 publications

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“…10 Therefore, BN is considered to be an ideal insulator for layered channel materials. Several studies of the optical, 11 mechanical, 12 phonon, 13 electrical tunneling, 14,15 oxidation resistance, 16 and hydrophobic 17 properties of BN have also been reported.…”

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confidence: 99%

Layer-by-Layer Dielectric Breakdown of Hexagonal Boron Nitride

Hattori

Taniguchi²,

Watanabe³

et al. 2014

ACS Nano

185

216

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Hexagonal boron nitride (BN) is widely used as a substrate and gate insulator for two-dimensional (2D) electronic devices. The studies on insulating properties and electrical reliability of BN itself, however, are quite limited. Here, we report a systematic investigation of the dielectric breakdown characteristics of BN using conductive atomic force microscopy. The electric field strength was found to be ~12 MV/cm, which is comparable to that of conventional SiO2 oxides because of the covalent bonding nature of BN. After the hard dielectric breakdown, the BN fractured like a flower into equilateral triangle fragments. However, when the applied voltage was terminated precisely in the middle of the dielectric breakdown, the formation of a hole that did not penetrate to the bottom metal electrode was clearly observed. Subsequent I-V measurements of the hole indicated that the BN layer remaining in the hole was still electrically inactive. Based on these observations, layer-by-layer breakdown was confirmed for BN with regard to both physical fracture and electrical breakdown. Moreover, statistical analysis of the breakdown voltages using a Weibull plot suggested the anisotropic formation of defects. These results are unique to layered materials and unlike the behavior observed for conventional 3D amorphous oxides.

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confidence: 99%

Layer-by-Layer Dielectric Breakdown of Hexagonal Boron Nitride

Hattori

Taniguchi²,

Watanabe³

et al. 2014

ACS Nano

185

216

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“…For instance, insulating hexagonal boron nitride (hBN) has emerged as an excellent substrate for graphene, yielding graphene devices with improved mobility and lower disorder compared with more conventional dielectrics 4 . Furthermore, hBN is atomically flat and, thus, it can serve as a uniform tunnelling barrier that allows perfectly planar charge injection 7 . Semiconducting molybdenum disulphide (MoS 2 ), another 2D material, shows a transition from an indirect band gap of 1.3 eV in the bulk to a direct band gap of 1.8 eV for a monolayer 6 .…”

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confidence: 99%

“…Furthermore, insulator (or tunnel barrier) and channel material with band gap, which should be ultrathin and stable, have been required for flexible and transparent memory applications. In this sense, the 2D materials, such as hBN and MoS 2 , can be great candidates thanks to their superior electrical and mechanical properties 4,7,25 .…”

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confidence: 99%

Controlled charge trapping by molybdenum disulphide and graphene in ultrathin heterostructured memory devices

et al. 2013

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Atomically thin two-dimensional materials have emerged as promising candidates for flexible and transparent electronic applications. Here we show non-volatile memory devices, based on field-effect transistors with large hysteresis, consisting entirely of stacked two-dimensional materials. Graphene and molybdenum disulphide were employed as both channel and charge-trapping layers, whereas hexagonal boron nitride was used as a tunnel barrier. In these ultrathin heterostructured memory devices, the atomically thin molybdenum disulphide or graphene-trapping layer stores charge tunnelled through hexagonal boron nitride, serving as a floating gate to control the charge transport in the graphene or molybdenum disulphide channel. By varying the thicknesses of two-dimensional materials and modifying the stacking order, the hysteresis and conductance polarity of the field-effect transistor can be controlled. These devices show high mobility, high on/off current ratio, large memory window and stable retention, providing a promising route towards flexible and transparent memory devices utilizing atomically thin two-dimensional materials.

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“…In conventional two dimensional semiconductor double layer structures, tunneling has shown remarkable features, including resonant tunneling, Coulomb correlations at high magnetic fields and Landau-level spectroscopy [3][4][5][6] . In the regime of 2D layered materials, hBN with a band gap of ∼ 5.9 eV 7 is an ideal candidate for an insulating barrier 8 . Recent studies on heterostructures with single and bilayer graphene as electrodes and hBN as the insulator have shown interesting features, including a very strong negative differential resistance (NDR) [9][10][11][12] .…”

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confidence: 99%

“…2a, where the non-ohmic behavior can be seen beyond V dc ≈ 0.2 − 0.3 V. While the red curve shows a clear NDR region in the negative voltage side, the effect is less pronounced in the positive side and for the blue curve. The voltage range probed is believed to be below the Fowler-Nordheim regime, where the barrier is essentially triangular, due to a very high applied bias 8 . In recent studies, NDR signatures were observed in single and bilayer graphene based heterostructures, which were attributed to resonant tunneling via momentum conservation when the energy bands of the top and bottom graphene layers were aligned 11,12 .…”

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confidence: 99%

Evidence for Defect-Mediated Tunneling in Hexagonal Boron Nitride-Based Junctions

et al. 2015

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We investigate tunneling in metal-insulator-metal junctions employing few atomic layers of hexagonal boron nitride (hBN) as the insulating barrier. While the low-bias tunnel resistance increases nearly exponentially with barrier thickness, subtle features are seen in the current-voltage curves, indicating marked influence of the intrinsic defects present in the hBN insulator on the tunneling transport. In particular, single electron charging events are observed, which are more evident in thicker-barrier devices where direct tunneling is substantially low. Furthermore, we find that annealing the devices modifies the defect states and hence the tunneling signatures.Van der Waals heterostructures, where layered stacks of two dimensional materials are embedded in precisely desired patterns, have gained immense attention in recent times 1,2 . Such tailor-made structures of graphene, hexagonal boron nitride (hBN), metal dichalcogenides and other 2D materials offer exotic device geometries to explore new physics. Tunnel junctions with an atomically thin insulator barrier sandwiched between atomic layers of 2D materials form an interesting structure in this respect. In conventional two dimensional semiconductor double layer structures, tunneling has shown remarkable features, including resonant tunneling, Coulomb correlations at high magnetic fields and Landau-level spectroscopy 3-6 . In the regime of 2D layered materials, hBN with a band gap of ∼ 5.9 eV 7 is an ideal candidate for an insulating barrier 8 . Recent studies on heterostructures with single and bilayer graphene as electrodes and hBN as the insulator have shown interesting features, including a very strong negative differential resistance (NDR) 9-12 . In all of these transport studies hBN is assumed to be a benign element. However, from a materials perspective there have been extensive efforts to understand the underlying structure and defect mechanisms in thin layers of hBN, which can have important consequences on electrical transport 13-15 . Here we present detailed tunneling transport measurements on simple junctions consisting of metal or graphite electrodes separated by a thin hBN layer. Our results demonstrate that the hBN insulator can yield unexpected transport signatures suggestive of defect-mediated tunneling processes.In a conventional metal-insulator-metal (M-I-M) junction, the tunnel current-voltage characteristic (I-V ) is linear at low biases, with the tunneling resistance inversely proportional to sample area and exponentially dependent on the barrier thickness d. Our studies show that the I-V with hBN as the barrier is distinct from such a simple behavior in various respects. Thinner barrier devices show a finite linear tunnel current at low biases and a roughly exponential dependence of the low bias resistance with d, complying with standard quantum mechanical tunneling, in agreement with previous reports 9,12 . However, in relatively thicker barrier devices, h--BN

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Electron tunneling through atomically flat and ultrathin hexagonal boron nitride

Cited by 446 publications

References 28 publications

Layer-by-Layer Dielectric Breakdown of Hexagonal Boron Nitride

Layer-by-Layer Dielectric Breakdown of Hexagonal Boron Nitride

Controlled charge trapping by molybdenum disulphide and graphene in ultrathin heterostructured memory devices

Evidence for Defect-Mediated Tunneling in Hexagonal Boron Nitride-Based Junctions

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